The present invention relates to a porphyrin metal complex having nitroimidazole group at the side chain thereof, and more specifically, to the porphyrin metal complex composed by connecting porphyrin metal complex which is used for missile therapy as drug delivery system (DDS), and nitroimidazole which is an effective radiosensitizer.
The present invention also relates to a contrast medium and a sensitizer used for diagnosis and/or treatment of cancer in magnetic resonance imaging (MRI) and/or radiotherapy, comprising of said porphyrin metal complex having nitroimidazole group at the side chain thereof, as an active ingredient.
Furthermore, the present invention relates to a porphyrin metal complex having a functional amino group capable of connecting with a physiologically active substance easily, for example anticancer agent, via an acidic functional group of said physiologically active substance such as carboxylic group, isothiocyanate group or azide group, at the side chain of the porphyrin complex, which is used for missile therapy.
As a new method of treatment for cancer, photodynamic fluorescent diagnosis and therapy (PDDT: Photodynamic Diagnosis and Therapy) has been performed. It is a method in which a certain type of porphyrin derivatives is administered to a subject by, for example, intravenous injection to retain the porphyrin derivative in the target cancerous tissues in the subject, followed by laser irradiation to fluorescent diagnose the cancerous tissues and cause selective destruction of said cancerous tissues. The therapy utilizes the two properties of a porphyrin derivative, i.e., longer retention time in cancerous tissues than normal tissues and photosensitivity of the porphyrin derivative.
For the past fifteen years, about 5,000 patients were treated of the malignant tumor by PDDT in the world, and PDDT has been fixed to be one of the methods for the treatment of caner. Many types of cancer are reported to be effectively treated by PDDT such as a cerebral tumor, a retina cancer, a cutaneous cancer, a cancer of the esophagus, sublimes vesical cancer and primary stage of lung cancer. Recently, PDDT has also been applied for fluorescent diagnosis of an endoscopy.
More recently, development of the treatment for cancer by DDS method applying the selective accumulability of porphyrin compound used in PDDT is reported. That is, the anticancer agent is connected to a porphyrin compound and accumulated to the cancerous tissues selectivity, and then, the essentially anticancer action of the drug is exhibited against the cancerous tissues directly. This method is expected to be the effective DDS therapy for the treatment of cancer instead of monoclonal antibody therapy.
The present inventors have synthesized more than 1,000 porphyrin compounds in order to develop the effective porphyrin compounds, considering the specific properties of these compounds, such as affinities, fluorescent and cell killing effects against the cancerous tissues, and reported the correlation between these affinities to cancerous tissues and the chemical structures (Modern Medicine, 1993, July; Asahi News Paper Co.,). Among them, certain porphyrin compounds were proposed to be a diagnosis and therapeutic agent for the photodynamic fluorescent treatment, a contrast medium for treatment of cancer in magnetic resonance imaging and neutron capture therapeutic agent. However, these porphyrin compounds were not specifically developed for applying to DDS therapy, and therefore, DDS effects of these compounds were not sufficient.
It is necessary for the porphyrin compounds to be the carrier of DDS therapy to connect with the porphyrin compound by covalence bonding, and to have the high functions such as affinity, fluorescent and cell killing effect against cancerous tissues in order to accumulate a physiologically active substance such as anticancer agent to the target tissues selectively and effectively.
By the way, radiotherapy is confirmed to be one of cancer therapies together with surgical treatment and chemotherapy; however, there are many problems in radiotherapy. For example, tumor is composed of approximately 20% of anoxic tissues and these anoxic tissues exhibit the resistance against the radioactive rays two to three times stronger than the normal tissues. Therefore, the presence of these anoxic tissues in the cancerous tissues is the main factor to prevent the improvement of radiotherapy and recurrence of tumor.
Accordingly, there have been developed drugs selectively elevating the radio-affinity of the anoxic tissues in tumor, and nitroazole derivatives having large electron affinities were proposed. Among them, nitroimidazoles were proposed to be effective drugs for radiosensitizers due to their sensitivities against an anoxic tissues, rapid metabolite rate and wide safety margin. Therefore, various nitorimidazole derivatives such as misonidazole have been developed.
Misonidazole, one of the representative compounds of sensitizer for anoxic tissues, exhibits twice times more efficacies in animal experiment implanting tumor compared with absence of this compound; however, it is difficult to administer effective dosage of this compound due to its high neurotoxin and no efficacy is observed in the case of the human being [Gan to Kagakuryoho (Tumor and Chemotherapy); vol. 8, 1656 (1981)].
On the contrary, the compound having fluorine atom at the certain position is awaited to be a medicine due to its mimic effect, its inhibition effect for metabolite and its increasing liposolubility. Based on this theory, nitroimidazole compound having fluorine atom in the molecular has been developed (Int. J. Radiation Oncology Biol. Phys., 16, 1045 (1989); ibid., 20, 1249 (1991); Japanese Patent Application Laid-open 2-76861). This nitroimidazole compound having fluorine atom in the molecular, however, shows low radiosensitizer effect even though elevating its radiosentisitizing effect and decreasing neurotoxicity. In general, imidazole type drugs may distribute to the whole organs of the living body and not specifically distribute to the cancerous tissues.
Therefore, this nitroimidazole compound having fluorine atom in the molecular has confirmed to be a drug having no selective accumulability to cancerous tissues.
The present inventors synthesized porphyrin compounds having an amino group in the molecular to achieve the selective accumulability to cancerous tissues. Further, they also synthesized porphyrin metal complexes connecting nitroimidazole using said porphyrin compounds, and proposed these porphyrin metal complexes as effective contrast medium for treatment of cancer in magnetic resonance imaging and radiosentisitizer of radiotherapy and PDDT therapy (Japanese Patent Application Laid-open No. 8-67682).
In the process for synthesizing the porphyrin metal complexes having nitroimidazole in the molecular, it is difficult to establish the practical production method because there is a problem in synthesize of carrier. That is, there are so many steps to obtain the porphyrin compounds having amino group in the molecular from protoporphyrin dimethyl ester as a starting compound. Furthermore, drastically hard conditions for oxidation and reduction processes have to be present in the synthetic route of the porphyrin compounds, and therefore, the yield of the compounds is low.
This compound has the functional amino group at the side chain thereof in which nitroimidozole type drug may connect with by covalent bond. Because amino group was closely located to the skeleton of porphyrin ring, it was influenced by xcfx80-electron of porpyhrin nucleus, and the amino group is not reactive. Add to above problems, decrease in the phtotoxicity of the compound is not sufficient.
The present inventors have investigated to obtain the porphyrin complex in which the complex functions well having good affinities, fluorescent and cell killing effects against cancerous tissues and applicable for DDS therapy without photo toxicity. As the results, they found out that the porphyrin derivative having amino group at the side chain thereof, which is obtained from protoporphyrin dimethyl ester by treating with HBr and condensed with one or two aminoalcohols having appropriate carbon atoms to introduce the functional amino group at the terminal of the side chain, is treated with metal such as manganese (Mn) to obtain porphyrin derivative without any phototoxicity, which is the specific toxicity of porphyrin derivatives.
Furthermore, the present inventors found out that porphyrin metal complex having nitroimidazole, which is more potential anticancer agent, at the side chain of the aforementioned porphyrin derivative via the functional amino group thereof, shows effective accumulability to cancerous tissues, and to be the sensitizer with contrast ability for radiotherapy in the MRI method.
Therefore, it is an object of the present invention to provide a porphyrin metal complex composed by connecting porphyrin metal complex, which is carrier for drug, and nitroimidazole which is an effective anticancer agent.
Furthermore, it is other object of the present invention to provide a contrast medium and a sensitizer used for diagnosis and/or treatment of cancer in magnetic resonance imaging (MRI) and/or radiotherapy, comprising said porphyrin metal complex having nitroimidazole at the side chain thereof, as an active ingredient.
It is still another object of the present invention to provide a porphyrin metal complex used for DDS therapy capable of connecting with a physiologically active substance easily as missile therapy.
To solve the above-mentioned objects, one aspect of the present invention provides a porphyrin metal complex represented by the following formula (I): 
[wherein,
when one of R1 and R2 is xe2x80x94CHxe2x95x90CH2 or xe2x80x94CH(CH3)xe2x80x94OH, the other is xe2x80x94CH(CH3)xe2x80x94Oxe2x80x94(CH2)nxe2x80x94NHxe2x80x94Ra; or both of R1 and R2 are xe2x80x94CH(CH3)xe2x80x94Oxe2x80x94(CH2)nxe2x80x94NHxe2x80x94Ra;
R3 is hydrogen atom or xe2x80x94COxe2x80x94(CH2)mxe2x80x94COOH;
M is transition metal of Mn, Fe, Co or Cu],
in which, Ra is hydrogen atom or the group represented by the following formula: 
n and m are the integer 2 or 3,
or a pharmaceutically acceptable salt thereof.
As more specific embodiment of the present invention, it is provided a porphyrin metal complex represented by the above formula (I) used for DDS therapy capable of connecting with a physiologically active substance easily as missile therapy, wherein;
when one of R1 and R2 is xe2x80x94CHxe2x95x90CH2 or xe2x80x94CH(CH3)xe2x80x94OH, the other is xe2x80x94CH(CH3)xe2x80x94Oxe2x80x94(CH2)nxe2x80x94NH2; or both of R1 and R2 are xe2x80x94CH(CH3)xe2x80x94Oxe2x80x94(CH2)nxe2x80x94NH2;
R3 is hydrogen atom;
n is the integer 2 or 3;
M is transition metal of Mn, Fe, Co or Cu],
or a pharmaceutically acceptable salt thereof.
As more specific embodiment of the present invention, it is provided a porphyrin metal complex having nitorimidazole at the side chain thereof represented by the above formula (I), wherein;
when one of R1 and R2 is xe2x80x94CHxe2x95x90CH2 or xe2x80x94CH(CH3)xe2x80x94OH, the other is xe2x80x94CH(CH3)xe2x80x94Oxe2x80x94(CH2)nxe2x80x94NHxe2x80x94Ra; or both of R1 and R2 are xe2x80x94CH(CH3)xe2x80x94Oxe2x80x94(CH2)nxe2x80x94NHxe2x80x94Ra;
R3 is hydrogen atom or xe2x80x94COxe2x80x94(CH2)mxe2x80x94COOH;
M is transition metal of Mn, Fe, Co or Cu],
in which, Ra is the group represented by the following formula: 
n and m are the integer 2 or 3,
or a pharmaceutically acceptable salt thereof.
Another aspect of the present invention provides a sensitizer used for diagnosis and/or treatment of cancer in magnetic resonance imaging (MRI) and/or radiotherapy, comprising of said porphyrin metal complex having nitroimidazole at the side chain thereof, as active ingredient.